1. Field of the Invention
The present invention relates to a wet image forming unit for forming a developed image by using a liquid developing solution containing toner particles and an image forming apparatus of an electrophotographic system having the image forming unit, more particularly, to a wet image forming unit having a squeeze roller for removing a surplus liquid developing solution from a photosensitive belt and an image forming apparatus.
2. Description of the Prior Art
Hitherto, an image forming apparatus of an electrophotographic system forms a developed image on a photosensitive body by steps of charging, exposing, and developing. Further, the developed image is transferred onto a recording medium by steps of transferring and fixing. As for a developing solution used in the developing step, there is a liquid developing solution having dispersing solution with toner particles. A wet image forming unit using the liquid developing solution forms the developed image on the photosensitive body to which an electrostatic latent image is formed.
In the conventional wet image forming unit, the electrostatic latent image formed on the photosensitive body is developed at an interval between the developing roller and a photosensitive belt by the liquid developing solution supplied from a developing solution supply port. Upon this development, the developing solution adhered to the photosensitive body excessively is squeezed by a squeeze roller. As a result, the image on the photosensitive belt is like a film and by a drying step, after that, transferred to a paper.
In the Official Gazette of Japanese Patent Application Laid-Open No. Hei 8-123207, a squeeze roller is rotated in the direction opposite to the rotational direction of a photosensitive body during development. As disclosed in the Official Gazette of Japanese Patent Application Laid-Open No. Hei 3-168783, a squeeze roller is rotated in the direction similar to the rotational direction of a photosensitive body during development. In those squeeze rollers, when the squeeze roller is rotated in the direction opposite to the photosensitive body during development, there is a fear that a developed image formed on the photosensitive body by a developing roller is disturbed and it is difficult that a pressure of the squeeze roller is set.
Consequently, in view of forming a stable developed image, as shown in the latter disclosure, it is more preferable that the squeeze roller is rotated in the direction similar to the rotational direction of the photosensitive body upon development. In this case, the same voltage potential as that of the developing roller which supplies a liquid developing solution to the photosensitive body is applied to the squeeze roller and, without disturbing the developed image formed by the developing roller, a surplus developing solution can be squeezed.
However, when the operation to squeeze the surplus developing solution by the squeeze roller is performed, a part of the surplus developing solution squeezed from the photosensitive body by the squeeze roller remains and gathers at an interval (gap) between the photosensitive body and the squeeze roller, which is located on the upstream side from the center of a portion where the photosensitive body and the squeeze roller contact. When the image forming apparatus is stopped while holding this state and left as it is, the developing solution which is gathering between the gap dries and congeals. Thus, this exerts a bad influence such that a stain causes upon next printing or the like.
If a force to press the squeeze roller to the photosensitive body so as to strongly rub during development is increased, the photosensitive body is damaged and broken, so that the life is shortened.
The conventional wet image forming unit as mentioned above has a problem that the liquid developing solution cannot be efficiently removed from the photosensitive body and the squeeze roller and a bad influence is exerted upon next printing.